Two-stage (initiation-promotion) carcinogenesis in vivo and in vitro.

After a short review on the two-stage (initiation and promotion) chemical carcinogenesis in vivo, the conditions required for its demonstration have been reported with several experimental data, showing the role of two distince agents, the initiator and the promotor. The same phenomenon has also been demonstrated with cell cultures in vitro. Rat embryo cells treated with an initiator and then submitted to the continuous action of a promotor have been transformed more rapidly than the untreated cells. Transformation has been tested essentially by the tumorigenicity of the cells. The results indicate that tissue culture cells are an appropriate system to investigate the mechanism of two-stage chemical carcinogenesis and allow the detection of the initiating and promoting potentialities of various compounds.